Fixes: #48945

Description:

The convert:to-title-case, convert:to-upper-camel-case, and
convert:to-lower-camel-case editor commands were stripping leading
whitespace from each line of a multi-line selection.

Root cause: The conversion functions split on whitespace using
.split_whitespace() and then joined the resulting words, discarding any
leading spaces/tabs before the first word on each line.

Fix: Each line now preserves its leading whitespace by capturing and
re-prepending it before applying the case conversion.

Tests: Added test cases covering multi-line selections with indentation
for all three commands.

Video : 


[bug1fix.webm](https://github.com/user-attachments/assets/f4d25c55-bc6d-44e6-a989-7d9b4bc59ac9)

Release Notes:

- Fixed trailing whitespace handling on text case changes